Method and device for switching wavelength division multiplexed optical signals using two-dimensional micro-electromechanical mirrors

ABSTRACT

A switch device and method is disclosed that is capable of switching wavelength division multiplexed optical signals. The device comprises a switch element that includes a two-dimensional micro-electromechanical mirror. The two-dimensional micro-electromechanical mirror is adapted to reflect an optical signal so that it is directed to a selected target. The switch element may also comprise a beam splitter and a plurality of wave plates. The beam splitter is adapted to transmit light in one polarization and reflect light in another polarization. The wave plates are adapted to change the polarization of the light so that the beam splitter either reflects or transmits the light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 09/826,982, filed on Apr. 4, 2001, now U.S. Pat.No. 6,532,115 incorporated herein by reference, which is acontinuation-in-part application of U.S. patent application Ser. No.09/716,196, filed Nov. 17, 2000, now U.S. Pat. No. 6,313,936. U.S. Pat.No. 6,313,936 is a continuation-in-part application of U.S. patentapplication Ser. No. 09/666,898 filed on Sep. 20, 2000 now U.S. Pat. No.6,580,845.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to optical switching and, moreparticularly, to an optical switching system, device, and method usingtwo-dimensional micro-electromechanical mirrors.

2. Description of Related Art

Optical communication systems are a substantial and rapidly growing partof communication networks. The expression “optical communicationsystem,” as used herein, relates to any system that uses optical signalsto convey information across an optical transmission device, such as anoptical fiber. Such optical systems may include, but are not limited totelecommunication systems, cable television systems, and local areanetworks (LANs).

While the need to carry greater amounts of data on optical communicationsystems has increased, the capacity of existing transmission devices islimited. Although capacity may be expanded, e.g., by laying more fiberoptic cables, the cost of such expansion is prohibitive. Consequently,there exists a need for a cost-effective way to increase the capacity ofexisting optical transmission devices.

Wavelength division multiplexing (WDM) has been adopted as a means toincrease the capacity of existing optical communication systems. In aWDM system, plural optical signals are carried over a singletransmission device, each channel being assigned a particularwavelength.

An essential part of optical communication systems is the ability toswitch or route signals from one transmission device to another. Forexample, micro-electromechanical mirrors (MEMs) have been developed forrouting signals between transmission devices. A discussion of MEMdevices can be found in K. E. Peterson, “Micromechanical Light ModulatorArray Fabricated on Silicon,” Applied Physics Letters, Volume 31, Page521 (1977). This technique operates by changing the angular orientationof the mirrors, thereby reflecting signals to different locations.

Designers have also considered using bubbles that are capable ofchanging their internal reflection for switching optical signals. Adiscussion of this can be found in “Compact Optical Cross-connect SwitchBased on Total Internal Reflection in a Fluid-containing PlanarLightwave Circuit,” by J. E. Fouquet, in Trends in Optics and PhotonicsSeries, A. Sawchuk, ed., Vol. 37, (Optical Society of America,Washington, D.C., 2000) pp. 204-206. However, these techniques areunable to switch between multiple wavelengths. Furthermore, both ofthese devices have limited switching speeds, in the range of 10 kHz forthe mirror devices and in the range of 100 Hz for the bubble devices.

Zigzag multiplexers are also well known in the art for transmittingsignals on multiple transmission devices. For example, U.S. Pat. No.6,008,920 discloses a multiplexer/demultiplexer device utilizing afilter that is sensitive to the angle of incidence of light. However,such multiplexers have not been used for switching or routingapplications in conjunction with arrays of fibers, detectors, andemitters.

Other switching approaches, such as the approach disclosed in U.S. Pat.No. 4,769,820, issued to Holmes, can switch data at GHz rates, which iseffectively switching at GHz transition rates. However, this approachrequires substantial optical switching power, has potential cross talk,and cannot resolve wavelength over-utilization issues. What is needed isa means for switching wavelength division multiplexed signals that iscapable of doing so at high speeds with no cross talk and requires lowswitching power. What is also needed is a switch device that is capableof switching large numbers of signals.

SUMMARY OF INVENTION

1. Advantages of the Invention

One or more embodiments of the present invention may achieve, but do notnecessarily achieve, one or more of the following advantages:

the ability to switch signals of different wavelengths;

the ability to switch signals at high speeds;

does not require high power;

has low crosstalk;

the ability to switch between wavelengths and fibers to avoidtransmission device or wavelength over-utilization;

the ability to broadcast to multiple transmission devices or couplerssimultaneously; and

the ability to efficiently switch a large volume of signals.

These and other advantages of certain embodiments of the presentinvention may be realized by reference to the remaining portions of thespecification, claims, and abstract.

2. Brief Description of One Embodiment of the Present Invention

The present invention comprises an optical switch element for use withat least one source and a plurality of targets. The source is adapted totransmit an optical signal to the optical switch device. The targets areadapted to receive the optical signal from the optical switch device.

The optical switch device comprises a beam splitter, a first wave plate,a direction altering device, and a second wave plate. The beam splitteris adapted to transmit light in a first predetermined polarization andreflect light in a second predetermined polarization. The first waveplate is positioned between the source and the beam splitter. The firstwave plate is adapted to alter the polarization so that it is reflectedby the beam splitter, wherein light transmitted by the source passesthrough the wave plate and is reflected by the beam splitter.

The direction altering device is positioned to receive light reflectedby the beam splitter and to selectively reflect light to a plurality ofpaths, the paths corresponding to the positions of the plurality oftargets. The second wave plate is positioned between the directionaltering device and the beam splitter. The second wave plate is adaptedto alter the polarization so that it is transmitted by the beamsplitter, wherein light redirected by the direction-altering devicepasses through the second wave plate and is transmitted by the beamsplitter.

The above description sets forth, rather broadly, a summary of oneembodiment of the present invention so that the detailed descriptionthat follows may be better understood and contributions of the presentinvention to the art may be better appreciated. Some of the embodimentsof the present invention may not include all of the features orcharacteristics listed in the above summary. There are, of course,additional features of the invention that will be described below andwill form the subject matter of claims. In this respect, beforeexplaining at least one preferred embodiment of the invention in detail,it is to be understood that the invention is not limited in itsapplication to the details of the construction and to the arrangement ofthe components set forth in the following description or as illustratedin the drawings. The invention is capable of other embodiments and ofbeing practiced and carried out in various ways. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purpose of description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is substantially a schematic diagram of one embodiment of aswitch device of the present invention.

FIG. 2 is substantially a schematic diagram of one embodiment of aswitch element of the present invention.

FIG. 3 is substantially a schematic diagram of one embodiment of aswitch element of the present invention illustrating one possiblephysical configuration of the switch element.

FIG. 4 is substantially a schematic diagram of one embodiment of thepresent invention in which a central processor is in communication witha plurality of switch elements.

FIG. 5 is substantially a schematic diagram of another embodiment of theswitch device of the present invention that utilizes a single sourceemitter.

FIG. 6 is substantially a schematic diagram of a prior art switch devicethat utilizes two micro-electromechanical mirrors.

FIG. 7 is substantially a schematic diagram of another embodiment of theswitch device of the present invention that utilizes twomicro-electromechanical mirrors and two wave plates.

FIG. 8 is substantially an alternate configuration of the embodimentillustrated in FIG. 7.

FIG. 9 is substantially an alternate configuration of the embodimentillustrated in FIG. 7.

FIG. 10 is substantially an alternate configuration of the embodimentillustrated in FIG. 7 that utilizes four wave plates.

FIG. 11 is substantially schematic diagram of one embodiment of theswitching element of the present invention.

FIG. 12 is substantially a graphical representation of the transmissionloss of the embodiment of FIG. 1.

FIG. 13 is substantially a graphical representation of the wavefrontquality impact on transmission of the embodiment of FIG. 1.

FIG. 14 is substantially a schematic diagram of another embodiment ofthe switching device of the present invention.

FIG. 15 is substantially a schematic diagram of one embodiment of ademultiplexing device of the present invention for use with a number ofoptical switching devices of FIG. 1.

FIG. 16 is substantially a schematic diagram of one embodiment of anoptical switching system of the present invention including a pluralityof switching devices shown in FIG. 1 used in conjunction withdemultiplexing device of FIG. 15.

FIG. 17 is substantially a schematic diagram of one embodiment of anoptical switch system of the present invention that utilizes an opticalisolation subsystem.

FIG. 18 is substantially a schematic diagram of one embodiment of anoptical switch system of the present invention including a subsystem toadjust the apparent angular size of the fiber array and the apparentangular spacing of the fibers.

FIG. 19 is substantially another configuration of the embodimentillustrated in FIGS. 7-10 that utilizes one micro-electromechanicalmirror.

FIG. 20 is substantially a detailed schematic diagram of one embodimentof a “two-dimensional” micro-electromechanical mirror that may be usedwith the present invention.

FIG. 21 is substantially a detailed schematic diagram of one embodimentof a mirror element of a micro-electromechanical mirror that may be usedwith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a part ofthis application. The drawings show, by way of illustration, specificembodiments in which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

Switch Device

As seen in FIG. 1, the present invention comprises a switch devicegenerally indicated by reference number 10. Switch device 10 may be usedin almost any optical communication system. Switch device 10 comprisessources and targets 12 and at least one switch element 26. Sources andtargets 12 comprise a source of incoming light signals and targets on towhich switch array 20 transmits outgoing signals. Sources and targets 12may be the same or different devices or objects. In the example shown inFIG. 1, sources and targets 12 are optical fibers 14. However, manyother devices and transmission mediums may be used. Sources and targets12 may include any number of fibers 14 and may use many different typesof fibers. Each optical fiber 14 comprises an end 16. Ends 16 arepreferably arranged in a two dimensional array, wherein the ends aresubstantially planar. It is recognized that the array may have manydifferent configurations, such as the square array shown in FIG. 1.

As an optical signal enters switch device 10 it is transmitted fromfiber end 16 through a collimating lens 24. Collimating lens 24collimates the light and transmits the signal to imaging lens 25 a.Imaging lens 25 a, together with other lenses, images the optical signalon to a bandpass filter 30. In the configuration illustrated in FIG. 1,one or more reflection devices or mirrors 27 a and 27 b are provided fordirecting the optical signal to the switch elements 26. As will bediscussed below, this configuration may allow switch device 10 to beconnected to additional switch devices, each switch device being adaptedto handle a set or range of wavelengths. However, it is recognized thatthe fibers 14 may be positioned differently to direct optical signals toswitch elements 26 without the need for mirrors 27 a and 27 b.

After the optical signal is reflected by mirrors 27 a and 27 b, thesignal passes through imaging lens 25 b, which, together with imaginglens 25 a, images the signal on a beam splitter or bandpass filter 30 a.Bandpass filter 30 a is preferably a narrow band filter that is adaptedto allow light within a predetermined range of wavelengths to passthrough the filter and reflect light outside the range of wavelengths.Such bandpass filters are available from JDS Uniphase in Santa Clara,Calif. The range of wavelengths is selected to correspond to the rangeof wavelengths in which switch element 26 a is designed to operate.Since many bandpass filters are sensitive to the angle of incidence, inthis embodiment each bandpass filter 30 preferably receives the opticalsignal at nearly normal incidence. The configuration of the componentsof switch device 10 allows for each bandpass filter 30 to be placed atnear normal incidence. The particular form of imaging, mentioned above,ensures that the phase at each bandpass filter 30 does not haveadditional focus, which would further degrade throughput because of thefilter's angular sensitivity. This particular form of imaging mayinclude 4-f or telecentric imaging, known to those skilled in the art.

If the incoming optical signal is not within the range of wavelengthsbandpass filter 30 a is adapted to transmit, the signal is reflected toa second bandpass filter 30 b and corresponding switch element 26 b. Inthe configuration shown in FIG. 1, additional imaging lenses 25 c and 25d and a mirror 27 c are provided for facilitating the transmission ofthe signal to the subsequent switch element 26 b. Together, imaginglenses 25 c and 25 d, which preferably incorporate a 4-f lens design ora suitable generalization that permits magnification, image the opticalsignal on to bandpass filter 30 b. This process of transmission orreflection is then repeated for each subsequent switch element 26 c-e.In this way, each switch element 26 receives signals in a range ofwavelengths that it is intended to receive and signals outside of thatrange are reflected to other switch elements.

This configuration allows switch elements 26 to be placed side by sidein a vertical configuration. This achieves several advantages. First,because bandpass filters 30 are transmissive in this design, dispersion,and attenuation are minimized for the reflected light that is incidenton many filters in sequence. Second, the approach shown in FIG. 1 usesfilters that are ostensibly at shallow angles, which decreasesundesirable angular sensitivity. Third, the approach shown in FIG. 1reduces cross talk from off-axis light.

The components of the present invention may be grouped into imagingunits that, for example, comprise a switch element 26 a, bandpass filter30 a, and imaging lenses 25 b and 25 c. Imaging units may be packagedindividually and installed and maintained separately.

Switch Element

Turning to FIGS. 2 and 3, each switch element 26 is arranged to receiveincoming light 32 from bandpass filter 30. As incoming light 32 entersswitch element 26, it is directed through an focussing lens 36 thatfocuses light signals on various components. In one embodiment, light 32then falls on beam splitter 38. Beam splitter 38 allows light 32 to passto detector array 42. Detector array 42 is adapted to detect signals inlight 32 and generate electrical signals based on the light signals.Detector array 42 may comprise many different well known devices, suchas 2609C Broadband Photodiode Module for both 1310 and 1550 nm detectionavailable from Lucent Technologies or InGaAs p-i-n photodiodes for1000-1700 nm detection, Part C30641E, available from EG&G. Theelectrical signals are transmitted to switch controller 44.

Switch controller 44 comprises a microprocessor 46 and memory 48.Microprocessor 46 is adapted to determine the intended destination ofthe light signal and route the signal to an appropriate fiber.Microprocessor 46 may be any of a number of devices that are well knownin the art. For example, microprocessor 46 may be an Intel Pentium IIIor other similar processor. Memory 48 is preferably random access memorythat also may be any of a number of devices that are well known in theart. Switch controller 44 may also comprise non-volatile memory 50 thatmay contain programming instructions for microprocessor 46.

Each light signal preferably carries a header that contains informationthat either identifies the signal or indicates its intended destination.This header information may be carried on a separate “control channel,”which may be a particular predetermined fiber or wavelength. Switchcontroller 44 is adapted to read the header. Switch controller 44 may beadapted, either alone or in coordination with other devices, todetermine the destination of the light signal. In order to avoidcontention for the same wavelength on the same optical fiber, whichwould result in interference when the signals are received, it may benecessary for each switch controller 44 to coordinate with other switchcontrollers. This may be facilitated by bus 52. Bus 52 is connected toeach switch element 26 and it allows each switch element to communicatewith a central controller 54 (not shown in FIG. 4).

As seen in FIG. 4, central controller 54 is in communication with eachbus 52 of each set 22 of switch elements 26. This allows centralcontroller 54 to receive signals from each switch element 26. Centralcontroller 54 may comprise a processor 60 that is adapted to performcomputer operations. Processor 60 is in communication with memory device62, which may be random access memory (RAM), and non-volatile memory 64,which is adapted to store data when power to controller 54 isinterrupted. Non-volatile memory 64 may be many different kinds ofmemory devices, such as a hard disk drive, flash memory, or erasableprogrammable read only memory (EPROM). Central controller 54 may be incommunication with a display device 66, such as a monitor or printer,and input device 68, such as a keyboard. Display device 66 and inputdevice 68 are adapted to allow an operator or user to communicate withswitch device 10 (see FIG. 1).

Central controller 54 may also comprise a communication device 70, whichmay be external or internal. Communication device 70 is adapted to allowcentral controller 54 to communicate with other devices, such as othercentral processors or a computer that controls the optical system.Communication device 70 may be many different types of devices that arewell known in the art, such as a modem, a network card, or a wirelesscommunication device.

Central controller 54 may utilize a number of different techniques forresolving conflicts between switch elements. These may include themethods discussed in co-pending patent application Ser. No. 09/666,898,filed Sep. 20, 2000. Alternatively, each switch element 26 may beadapted to resolve conflicts or interferences internally. Switchcontroller 44 may have its own destination table and transmission table,and it can be programmed to manage signals entering switch element 26.If each switch element 26 is assigned to handle a specific wavelength orrange of wavelengths, coordination between switch elements may not benecessary. However, some degree of coordination may be desirable.Therefore, a relatively low-bandwidth data connection to centralprocessor 54 (see FIG. 3) may be provided.

It is also recognized that it may be desirable to provide some form ofcommunication device, such as bus 52, to update switch controller 44.For example, if a fiber has been disconnected from the network, switchcontroller 44 would need to be informed that this fiber is no longeravailable for transmission. In addition, switch element 26 may also be anode from which data is downloaded. This would necessitate transmissionof data from each switch element 26 to another device to make use of theinformation.

In switch mode, once controller 44 has determined the destination of theoptical signal, the controller causes at least one emitter in emitterarray 56 to transmit an outgoing signal 28. The position of the emittercorresponds the position of the target of the signal. Outgoing opticalsignal back along the general path of the incoming signal. Returning toFIG. 1, in the case of switch element 26 a, outgoing signal 28 passesthrough bandpass filter 30 a, imaging lens 25 b, mirrors 27 a and 27 b,imaging lens 25 and, collimating lens 24 and is received by at least onetarget 12.

It is also recognized that a plurality of detector and emitter arraysmay be used in one switch element to detect and emit a plurality ofwavelengths. This would allow one switch element to perform the samefunction of an array of switch elements. Thus, the switch device of thepresent invention may comprise only a single switch element. The sameresult could be obtained by using single detector and emitter arraysthat are adapted to detect and emit a plurality of wavelengths.

Single Source Emitter Switch Element

As seen in FIG. 5, the present invention comprises an alternativeembodiment generally indicated by reference number 426. As incominglight 432 enters switch element 426, it is directed through focusinglens 436. In this embodiment, light 432 then falls on beam splitter 438.Beam splitter 438 reflects light 432 to detector array 442. Detectorarray 442 is adapted to detect signals in reflected light 432 and, asmentioned above, detector array 442 is capable of distinguishingdifferent signals that are being transmitted by different sources.Detector 442 may generate electrical signals based on the light signals.The electrical signals are transmitted to switch controller 444.

Switch controller 444 may be similar to switch controller 44 with amicroprocessor and memory (not shown). The microprocessor is adapted todetermine the intended destination of light signals and route thesignals to an appropriate fiber. As in the previous embodiment,conflicts or interferences between signals can be handled within switchelement 426.

Switch element also comprises an emitter 456 that is adapted toconstantly transmit light 458 over a period of time. The light isproduced in a desired range of wavelengths. Light 458 is transmitted tolens 460, which is adapted to collimate the light. Light 458 may thenpass through optional lenslet array 462, which is adapted to concentratethe light on individual modulators in modulator array 464. Theindividual modulators in modulator array 464 may be modulators that arewell known in the art, such as lithium niobate modulators available fromOrtel in Azusa, Calif. Modulator array 464 is in communication withcontroller 444, which may drive individual modulators to allow light topass through the array. The position of the individual modulatorscorresponds to the position of targets for the light 458.

By driving an individual modulator to allow light to pass through themodulator at selected times, the modulator can produce an outgoingoptical signal 428. The signal passes through beam splitter 438 and lens436 and is transmitted to a predetermined target.

Micro-Electromechanical Mirrors Switch Element

The present invention also comprises an embodiment that utilizesmicro-electromechanical mirrors (MEMs). MEMs are well known in the art,an example of which has been produced by Lucent Technologies in MurrayHill, N.J. MEMs are mirrors that may be selectively positioned in aplurality of positions. This allows the MEMs to reflect lighttransmitted from a source to a plurality of locations or targets. Aplurality of MEMs may be placed in an array to switch light from aplurality of sources.

As seen in FIG. 6, MEMs can be used to switch light spatially using whatis called a “3D” or “beamsteering” approach. In this approach, a firstMEMs array 300 is positioned to receive a plurality of incoming parallellight beams 300, sometimes called “pencil beams,” from a source orsources 304. Before light falls on a particular MEM, the MEM ispositioned or aimed to reflect light along a selected path. The path ofthe light corresponds to a location of a particular target 306 among aplurality of targets.

For some targets, such as an optical fiber, it is desirable that lightbeing transmitted to the target be substantially parallel to the normalaxis of the target. If first MEM array 300 were to reflect lightdirectly to a target, it may cause the light to be non-parallel to thenormal axis of the target. This is so because each MEM on array 300 maynot be aligned with the intended target and it is necessary to reflectlight at an angle relative to the path of the incoming light. To addressthis problem, a second MEM array 308 is provided. First MEM arrayreflects light 310 to a MEM on second MEM array 308. The particular MEMon second MEM array 308 is aligned with the axis of the desired target306 and the MEM is positioned so that light reflected by it is parallelto the preferred axis of the target.

A lenslet array 314, which may comprise an array of lenses, may beprovided between second MEM array 308 and target 306 to focus the lighton the respective target. A controller may also be provided (not shown)for controlling the position of the individual MEMs in the MEM arrays.

The present invention comprises embodiments that utilize MEMs to switchoptical signals. These embodiments utilize polarization of light signalsto selectively reflect and transmit light. Polarization is a well-knownproperty of light. There are two polarization states, typically denotedx and y, in which the electric field of the light oscillates in the x ory direction, respectively, as it propagates in the z direction. Suchlight is called linearly polarized x or y light, respectively.

Light of different polarizations can be superposed, i.e., added, so thatstates of polarization ax+by are possible. Furthermore, a and b can becomplex; a complex part denotes a phase lag or lead between the twopossible states. In particular, a polarization state x+iy, i=(−1)^(½),corresponds to a polarization state that rotates in the positive anglesense as it propagates and therefore is called right-circularlypolarized. The state x−iy corresponds to rotations of the electric fieldthat rotates in the negative angle sense, and is called left-circularlypolarized.

Light can be switched from one polarization state to another usinghalf-wave and quarter-wave wave plates, which are well known to thoseskilled in the art. A quarter-wave plate applies an additional factor ofi (one-quarter of a full wave) to the y state, converting x+y to x+iy,or converting x+iy to x−y. Similarly, a half-wave plate applies a factorof −1 (one half of a full wave) to the y component, converting x+y tox−y. These facts are used in the embodiments described below.

Additionally, it is well known to those skilled in the art thatpolarizing beam splitters can reflect one linear polarization, forexample, x, and transmit the second linear polarization state, y. Thesedevices may be used to reflect or transmit light depending on thepolarization of the light.

Turning now to FIG. 7, the present invention also comprises analternative switch element generally indicated by reference number 350.Circularly polarized light 352 is transmitted by source 353. In theexample calculations that follow, incoming light 352 is assumed to beright polarized light. Light 352 passes through lens 354, which focusesthe light onto image plane 356. The light is allowed to diverge from theimage plane until the light from the individual sources is of a sizethat matches the size of the individual micro-mirrors on MEMs array 366.Light 352 then passes through a lenslet array 358 that is adapted tocollimate the light, i.e., make it into a “pencil beam” that neitherdiverges nor converges.

A beam splitter 357 may be provided in the path of incoming light 352 toreflect a portion of the incoming light to a detector array 388.Detector array 388 is adapted to convert the light signal to electricalsignals and transmit the signals to controller 382. Controller 382,similar to controllers in the embodiments discussed above, is adapted todetermine the destination of the incoming signal and drive MEM arrays366 and 370 to route the signal to the appropriate target 386. Asdescribed above, each optical signal may be provided with a header thatallows controller 382 to determine the destination of the signal. A timegap may be provided between the header and the rest of the signal toprovide sufficient time for controller 382 to determine the destinationand drive particular MEMs in MEM arrays 366 and 370 to their desiredangular positions.

After passing through lenslet array 358, light 352 passes through λ/4plate 360. This converts the right-circularly polarized light from astate x+iy to x−y. The state x−y is a purely linearly polarized state oflight in a 45 degree direction, and will be denoted by x′. A properlyoriented polarizing beam splitter 362 will then reflect the x′-polarizedlight to MEM array 366.

Reflected light 364 is transmitted to a particular MEM 367 that isaligned with the particular source 353 that emitted incoming light 352.MEM 367 is angularly positioned by controller 382 to reflect the lightto a particular MEM 371 on MEM array 370. MEM 371 is aligned with aparticular target 386 in a plurality of targets 384. It is recognizedthat targets 384 may be the same devices as sources 351. MEM 371 isangularly positioned by controller 382 to reflect incoming light 368 totarget 386. The angular position of MEM 371 depends on the position ofMEM 367 on MEM array 366. MEM arrays 366 and 370 are oriented so thatthe light passes through free space in this embodiment.

Reflected light 372 then passes through a λ/2 plate, which converts thepolarization of the incident light from x′=x−y to y′=x+y, which is anorthogonal to x′. The light is then reflected by mirror 376. Reflectedlight 380 passes through lens 378, which acts to image the input lensletarray to the output lenslet array. Light 380 then passes through, ifnecessary, polarizing beam splitter 362. After passing throughpolarizing beam splitter 362 by virtue of its y′ polarization, it thenreturns to the original λ/4 plate, which converts the y′=x+y polarizedlight to a polarization state x+iy, i.e., identical to the originalinput polarization state. Light 380 then exits the switching element thesame way it came in, and proceeds to target 386.

FIGS. 8 and 9 illustrate embodiments that operate in substantially thesame way as the embodiment illustrated in FIG. 7. In the embodimentshown in FIG. 8, MEM array 370 is on the same side of switch element 349as MEM array 366. In switch element 348 in FIG. 9, MEM array 370 ispositioned in line with polarizing beam splitter 362 and targets 384.Thus, mirror 376 (seen in FIGS. 7 and 8) is not required.

FIG. 10 illustrates an embodiment that utilizes four λ/4 plates 360,392, 394, and 396. Light 352 is focused, converted, reflected asdescribed above. However, a λ/4 plate 392 between beam splitter 362 andMEM array 366 is used to convert the polarization state from x′=x−y tox−iy. Light 364 impinges on MEM array 366 as before and then propagatesback through quarter-wave plate 392, which then converts thepolarization from x−iy to x+y=y′. Thus, light 398 becomes orthogonallypolarized and passes through polarizing beam splitter 362 to MEM array370.

Individual beams are directing the light in many different directionsafter being reflected by MEM array 366, and if these directions arelarger than about 10 degrees from normal incidence at quarter-wave plate392 and at polarizing beam splitter 362, significant errors in thepolarization state of the light may occur. Thus, reflection angles arelimited in this embodiment to less than about 10 degrees from normalincidence.

After light 398 passes through polarizing beam splitter 362, the lightpasses through a third quarter-wave plate 394 that converts thepolarization state from y′=x+y to x+iy. The light 398 then proceeds toMEM array 370, which performs the same functions as in the previousembodiments. Reflected light 399 passes through the third quarter-waveplate 394 where its polarization state is changed from x+iy to x′=x−y.

By virtue of this new polarization state, the light is now reflected bythe polarizing beam splitter upwards towards a fourth quarter-wave plate396 that converts the polarization state from x′=x−y to x−iy. Light 397then passes through lens 378, reflects from mirror 376 back through thelens. Lens 378 focal length is chosen so that the double transmission ofthe light results in imaging lenslet array 358 onto it self, similar towhat was done in the embodiment shown in FIG. 7.

Light is again incident on fourth λ/4 plate 396, which now converts thepolarization state from x−iy to y′=x+y. By virtue of this newpolarization state, light 380 transmits through polarizing beam splitter362 and then passes out switching element 390 in the same manner asdescribed in the previous embodiment.

Two-dimensional MEM Switch Element

FIG. 19 discloses an alternative preferred embodiment that utilizes a“two-dimensional” direction altering device. As in previous embodiments,source 353 transmits incoming light signal 352. A portion of incominglight 352 is transmitted by beam splitter 357 through lens 354, whichfocuses the light onto image plane 356. The light is allowed to divergefrom the image plane until the light from the individual sources is of adesired size. Light 352 then passes through a lenslet array 358 that isadapted to collimate the light, i.e., make it into a “pencil beam” thatneither diverges nor converges. After passing through lenslet array 358,the light is reflected by beam splitter 362 to a direction alteringdevice 902. Direction altering device 902 may be a number of devicesthat are known in the art for redirecting light, such as MEMs, bubblesof gas, or acousto-optic devices. In the description of the embodimentthat follows, the direction altering device 902 shall be referred to asa MEM array.

A portion of incoming light 352 may be reflected by beam splitter 357 todetector array 388. Detector array 388 is adapted to convert the lightsignal to electrical signals and transmit the signals to controller 382.Controller 382, similar to controllers in the embodiments discussedabove, is adapted to determine the destination of the incoming signaland drive MEM arrays 902 to route the signal to the appropriate target386. As described above, each optical signal may be provided with aheader that allows controller 382 to determine the destination of thesignal. A time gap may be provided between the header and the rest ofthe signal to provide sufficient time for controller 382 to determinethe destination and drive a particular mirror in MEM array 902 to areflective position.

In this embodiment, MEM array 902 is a so called “two-dimensional”array. Two dimensional MEM arrays are well known in the art, adiscussion of which can be found in IEEE Communications Magazine, March2002, by Dobbelaere, Falta, Fan, Gloeckner, and Patra. As seen in FIGS.20 and 21, incident light 364 travels in a plane that is parallel to thesubstrate of MEM 902. All except one of the individual mirrors 904 in arow are in a down or lowered position, thereby allowing light 364 topass over them. However, controller 382 has selected one of the mirrors906 to reflect the light. Selected mirror 906 corresponds with theposition of one or more targets 386.

As seen in FIG. 21, controller 382 causes selected mirror 906 to movefrom a down position to an up or active position where it can reflectincident light 364. Selected mirror may be actuated using a number ofdifferent methods and devices, such as comb drives, thermal expansionactuators, electrostatic scratch drive actuators, and gap-closingelectrostatic actuators.

In the example shown in FIGS. 19 and 20, light is reflected in a 90degree angle. However, MEM array 902 may be designed to reflect light indifferent angles and the architecture of switch element 900 may bemodified accordingly.

Additionally, if all the mirrors in a row of two-dimensional MEMs 902 ofFIG. 20 are in the lowered position, the incident light will pass overthe entire array and can be detected by a detector 903 with suitableoptics at the far side of the substrate. This particular operation isreferred to as “dropping a channel,” and may be of benefit in somecases. If all the mirrors in a column of two-dimensional MEMs 902 ofFIG. 20 are in the lowered position, light can be injected from a sourceinto the outgoing path at that column by an emitter array 905 withsuitable optics at the lower side of the substrate. This particularoperation is referred to as “adding a channel,” and may be of benefit insome cases. Both detector 903 and emitter 905 are in communication withcontroller 382, which is adapted to read the detected signals and causeemitter 905 to emit appropriate signals.

Reflected light 368 is transmitted to mirror 908. The light is thenreflected by mirror 376. Reflected light 380 passes through lens 378,which acts to image the input lenslet array to the output lenslet array.Light 380 then passes through beam splitter 362, lenslet array 358, lens354 and beam splitter 357. Light 380 then exits the switching element totarget 386.

As in disclosed in previous embodiments, λ/4 plates 360 and 374 may beprovided for allowing bi-directional communication. If λ/4 plates 360and 374 are used, beam splitter 362 would be a polarizing beam splitterthat reflects light in one polarization and transmits light in anotherpolarization.

Similar to the embodiment disclosed in FIGS. 7-10, switch element 900may be utilized in an array of switch elements (not shown in FIG. 19). Adichroic beam splitter may be provided between the switch element 900and sources 353 to reflect light of a predetermined wavelength to theswitch element and to transmit light not in the predetermined wavelengthto other switch elements.

Positioning and Alignment of Switch Device

Returning to FIG. 1, switch elements 26 and fibers 14 are preferablyarranged substantially vertically so that switching elements 26 andfiber bundle 12 can be inserted vertically. The vertical configurationis advantageous for ease of access to switching elements 26 and for easeof alignment. Referring to FIG. 11, this is accomplished by providingeach switch element 26 with a 3-point kinematic alignment unit 514.Alignment unit 514 may comprise a prism 516, positioned between thefocusing lens 512 and an associated switch element 26. Prism 516 is usedto redirect the incident light to vertical for the embodiment shown inFIG. 1, and will not cause significant chromatic dispersion because thelight has a very narrow spectral bandwidth as it enters each switchingelement 26. In this embodiment, a power and data cable 518 is attachedto switch element 26 at a point that is directly above the center ofgravity of the switch element. This helps reduce the effect of forcesimparted by power cable 518. Wireless data ports 520 may also beprovided, thereby eliminating the need for a physical data connection.

In terms of structural positioning, some specific numbers determine theconfiguration of switch device 10. First, the required nominal angle ofincidence of an incoming signal is approximately 3.0 degrees to maintaina 0.4 nm of spectral shift or less for a bandpass filter designed fornormal incidence at 1500 nm mean wavelength. Within this 3 degrees,contributions come from the nominal incidence angle as well as fromoff-axis propagation of the light from the various optical carriers 14.Consider, for example, a situation where a circular fiber bundle 14 is64 fibers across and each fiber is separated by 100 microns. Theresulting radius (r) of the bundle 12 is 3.2 millimeters. The light fromthis bundle 12 is collimated to about 1 centimeter beam radius (w)because the fiber numerical aperture (NA) is about 0.1. The requiredfocal length (f) of the collimating lens 24 is about w/NA=10 cm. Thegreatest off-axis angle at collimating lens 24 is, therefore, aboutr/f=0.032 radians, i.e., about 1.9 degrees. This then leaves an angle θof about 1.1 degrees, worst case, for the nominal pointing angle. Using1.1 degrees as the angle of incidence on the bandpass filters 30 resultsin a 2.2-degree full angle (θ) between incident and reflected light. Atthis angle and with the imaging lenses 25 fitting with a 20% margin,results in a length of 1.2*w/(θ*π/180)=32.1 cm from imaging lens 25 toeach bandpass filter 30. Hence, the total length is about double, i.e.,64.2 cm, between mirrors 27 and bandpass filter 30. This length can bereduced if additional signal loss can be tolerated. Focusing lens 25 canconveniently be selected to have a focal length equal to the separationfrom the lens 25 to corresponding bandpass filter 30. Each switchingelement 26, including detector, emitter, and beam splitter, preferablyoccupies a region that is about 100 cubic cm or less.

Using the above-described approach, a large number of wavelength bandscan be sequentially demultiplexed. The limiting effects in thisembodiment are beam quality and transmission losses. As shown in FIG.12, for each switching element 26, six (6) surfaces are encountered.Each of the surfaces may have 0.1% transmission loss or less, based onmodern manufacturing capabilities, except for bandpass filters 30, whichtypically have about 15% loss in transmission, and about 1% loss inreflection. Hence, the loss versus number of switching elements M insequence is 0.85×(0.9995⁵×0.99)^(M). A plot of the signal transmissionversus number of switch elements M is given in FIG. 12, as well as acase in which the filters have a much worse loss of 15% per element uponreflection. From FIG. 12, it can be seen that even as many as 35switching elements can be sequenced with less than 3 dB loss for allelements, for the nominal 1% per filter. On the other hand, if eachfilter loses 15%, only about 14 switching elements can be sequenced withless than 10 dB loss for all elements.

Beam quality is also an important issue in determining the number ofswitching elements 26 that can be sequenced. For thelow-spatial-frequency aberrations expected for the 1 cm optics commonlyin use, the formula for power loss is plotted in FIG. 13. For this plot,the following is assumed: 1) 0.1, 0.05, and 0.025 waves rms error peroptical element, and 2) these errors combine in root mean square. It isalso assumed that switch element detectors 42 are 30 microns in size,that the wavelength is 1.5 microns, and that the F/# of lens 36 is 10,in accord with the assumptions above. The results for 0.05 rms waves peroptic, or better, will provide 3 dB of loss on average for the 28^(th)switching element. Less loss occurs for earlier switching elements inthe sequence.

Overall, the combined effect of transmission and wavefront quality withthe assumed values (0.05 waves or less, 1% or less for filters, 0.1% orless for other optics) leads to a 6 dB loss, or better, with 30switching elements in sequence. The overall result is therefore that upto 30 switching elements may be sequenced with reasonable losses.

FIG. 14 illustrates an alternative configuration of switch device 10 inwhich each bandpass filter 30 is angled to receive the optical signal ata substantially non-normal incidence. In this case, each switchingelement 26 receives the optical signal from a substantially verticaldirection, and, therefore, does not require prism 516 (see FIG. 11) foreach switching element 26. However, this embodiment suffers fromunsymmetrical paths between imaging lenses, which requires relocation ofthe imaging lenses in an arrangement that may be more difficult toalign.

Referring to FIGS. 15 and 16, the present invention includes system 600that is adapted to perform wide band demultiplexing. System 600 directsoptical signals having a predetermined range of wavelengths to anappropriate bank 500. Each bank 500 (similar to switch device 10 ofFIG. 1) comprises a plurality of switching devices 26. System 600includes a plurality of directing units 602. Each directing unit 602includes a first imaging lens 604 and a second imaging lens 606, amirror 608 for reflecting an optical signal from the first imaging lens604 to the second imaging lens 606, and a bandpass filter 610. Eachbandpass filter 610 is preferably a wide-band type filter configured toreceive an optical signal from second imaging lens 606 and allow anoptical signal within a predetermined range of wavelengths to passthrough the bandpass filter to bank 500 of optical switches (see FIG.16). An optical signal outside of the predetermined range of wavelengthsis reflected to another, subsequent directing unit 602. Element 609 maybe a bandpass filter or a fold mirror depending on the angular alignmenttolerances of bandpass filter 610 a.

Each bandpass filter 610 may divert, for example, groups of up to thirty(30) wavelengths. For instance, if the wavelength spacing between bandsis 0.8 nanometers, then the total wavelength range for one group is 24nanometers, and this entire group of thirty (30) wavelength bands issent to one bank 500 of switch elements.

Clearly, this alternative embodiment will introduce additional losses,but because the filter 610 bandwidths are rather wide, the losses forsequencing in this case are less than that for the individual switchingdevices 500. In this way, many different wavelengths can besimultaneously switched. For example, as noted in FIG. 16, it is notunreasonable to use 25 different switching banks 500, with an associatedadditional 3 dB of loss for the furthest bank 500 (with signalregeneration, the signal strength can be arranged to be nearly equal forall the bands upon exiting the system). The combination of twenty-five(25) banks 500 and thirty (30) wavelengths per bank 500 leads to 750wavelength bands. If 0.4 nanometers is used per band, the total bandpassused is 300 nm, which is essentially the entire telecommunications bandfrom 1360 n to 1560 nm.

One layer of the resulting optical switching system 700 is shownschematically in FIG. 16. In this case, demultiplexing system 600 isoriented perpendicular to the individual switching devices 500. Asindicated, a number of banks 500 may be located adjacent to one another(into the page). In this case, where twenty-five (25) banks 500 areprovided, the overall system 700 occupies about 40 cm wide×85 cmhigh×125 cm long. The latter length assumes 5 cm of thickness per bank500. Note that the system shown in FIG. 16 has a total of π*32²=3216input carriers, and 750 input wavelengths. If one assumes 10Gigabits/sec input per wavelength, the resulting throughput is then 24Petabits/sec. Accordingly, this embodiment has a tremendous capacity forswitching or routing data.

Faraday Rotator Embodiment

In an alternative embodiment, polarization is more carefully controlledand used for added redundancy of processing. This is performed byplacing a polarizing beamsplitter 702, a Faraday rotator 704, and oneadditional quarter-wave plate 706 between the input collimating lens andthe rest of the system, as shown in FIG. 17. Polarizing beamsplitter 702reflects one linear component, say x, and transmits the orthogonallinear component, y, into the switching system. The reflected light fromthe polarizer may be sent to a second, redundant switch array that issimilar to the first array (the array 500 of FIG. 16, for example), andthis second array is used to switch those signals for which thereflected light is stronger than the transmitted light, or to switchlight in case of failures in the first switching array.

Faraday rotator 704 rotates the polarization of the light inpolarization y to y′=x+y, and this light enters the first quarter-waveplate 706. λ/4 plate 706 then converts the light to right-circularlypolarized light x+iy, which is then propagated to the relevant switchelements 26. In some embodiments, a second quarter-wave plate 708 isprovided in front of each switch element 26. Second quarter-wave plate708 will convert light to linear polarization x′=x−y. The linearpolarization x′ is then reflected or transmitted to a detector array orto a MEMs array. If an embodiment is used with detectors, lightbackscattered from the detectors will be predominately light of the samepolarization and will therefore pass back through and out of the opticalsystem. This is evident to those skilled in the art because of thecombination of the polarizing beamsplitter and the Faraday rotator atthe fiber array. Faraday rotator 704 and two quarter-wave plates 706 and708 along the optical path are equivalent to a standard optical isolatorcomprising a polarizing beamsplitter, a Faraday rotator, and a half-waveplate.

Light emitted from the emitters, modulators, or exiting the MEMs arrayswill pass back through the polarizer in the orthogonal polarization,y′=x+y. This light will then be converted by the quarter wave plate 708at switch element 26 to right-circularly-polarized light x+iy. Thislight will then be transmitted back through the system to firstquarter-wave plate 706 where it will be converted to polarization statex′=x−y. This light then passes through Faraday rotator 704 a second timeand the light is converted to state −y by the rotator. This state oflight is transmitted through the polarizer and then passes through thecollimator on to the fiber array, as desired. Note that if the range ofwavelengths are significant, then dispersion in first quarter-wave plate706 may be an issue. Dispersion compensation can be added as needed byvarious means known to those skilled in the art.

In an embodiment where the intervening optics' properties varysignificantly (>10%) with linear state of polarization, additionalconsideration is required. Typically, one polarization state ispreferred over another. In such cases, the light transmitted through theoptical system from fiber array 14 to switching elements 26 is put intothe preferred linear polarization state. In this case, firstquarter-wave plate 706 near Faraday rotator 704 is moved to theswitching elements and combined with the quarter-wave plates 708 at therespective switching elements. The combination of the quarter-waveplates form half-wave plates at the respective switching elements forequivalent functionality.

Beam Contractor

In another embodiment of the present invention, it is desired to put thefiber array into as small a region as possible to enable the system toachieve better imaging performance over the entire array. Becauseimaging performance is a function of field angle, it is desired to putthe array into as small an angular region θ_(ar) as possible, as seenfrom the collimating lens. Some reduction of the extent of the array canbe achieved by fiber packaging means. These packaging means are wellknown to those skilled in the art, and are produced by companies such asHaleos (web site www.haleos.com). On the other hand, much moreflexibility in reduction can be achieved using optical system 800 shownin FIG. 18. In this Figure, a beam contractor 802 is used to form asmall image of the fiber array, followed by a lenslet array 804 toadjust the numerical aperture of the light entering or exiting eachfiber. Beam contractor 802 reduces the apparent width w of the array bya magnification factor M from the true width W, so that w=W/M.

Lenslet array 804 then adjusts the numerical aperture NA to NA1. Theresulting focal length changes from L=r/(NA×M) to L1=r/NA1, where r isthe clear radius of the lens, NA is the fiber numerical aperture, andNA1 is the adjusted numerical aperture. The resulting full angularextent of fiber array 14 is reduced from (W×NA)/r to (w×NA1)/r. Thisapproach is used to reduce the apparent angular extent of fiber array 14until the apparent angular separation of neighboring fibers is no lessthan about 3 times the diffraction limit of the collimating lens, inorder to limit-fiber-to-fiber crosstalk. The diffraction limit is givenby 1.22 λ/r, where λ is the longest wavelength of the light from thefiber array. As an example of the application of these techniques,assume that r=0.5 cm, and that λ=1.55 microns. The resulting neededangular separation is about 0.380 milliradians. Choose the full angularextent of the image of the fiber array, (w×NA1)/r, to be less than orequal to 2 degrees for best imaging performance. The resulting number offibers across the imaged region is then (2 degrees)×(17 milliradians perdegree)/0.38 milliradians=90 fibers across the diameter. Thecorresponding number of fibers that fit within a circular aperture witha diameter of 90 fibers is equal to 6360. Assuming switching between6360 fibers and 750 wavelength and 10 Gbps per wavelength, one findsthat routing of 47.7 Petabits per second of data can be supported withthis optical architecture.

CONCLUSION

Although the description above contains many specifications, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of presently preferredembodiments of this invention. Thus, the scope of the invention shouldbe determined by the appended claims and their legal equivalents ratherthan by the examples given.

What is claimed is:
 1. An optical switch element for use with at least one source, the source being adapted to transmit an optical signal to the optical switch element, and a plurality of targets, the targets being adapted to receive the optical signal from the optical switch device, the optical switch device comprising: (A) a beam splitter, the beam splitter being adapted to transmit light in a first predetermined polarization and reflect light in a second predetermined polarization; (B) a first wave plate positioned on an optical path between the source and the beam splitter, the first wave plate being adapted to alter polarization of the light transmitted by the source so that it is reflected by the beam splitter, wherein light transmitted by the source passes through the wave plate and is reflected by the beam splitter; (C) a micro-electromechanical mirror positioned to receive light reflected by the beam splitter, the micro-electromechanical mirror being adapted to selectively reflect light in a plurality of paths, the paths corresponding to the positions of the plurality of targets; (D) a second wave plate positioned on an optical path between the micro-electromechanical mirror and the beam splitter, the second wave plate being adapted to alter polarization of the light reflected by the micro-electromechanical mirror so that it is transmitted by the beam splitter, wherein light reflected by the micro-electromechanical mirror passes through the second wave plate and is transmitted by the beam splitter.
 2. The optical switch element of claim 1, further comprising a controller in communication with the micro-electromechanical mirror, the controller being adapted to determine a target for an optical signal and cause the micro-electromechanical mirror to reflect the signal to the target.
 3. The optical switch element of claim 2, further comprising a detector positioned to receive light from the source and in communication with the controller, the detector being configured to allow the controller to receive information from an optical signal.
 4. The optical switching element of claim 1, further comprising a lenslet array between the source and the beam splitter, the lenslet array being adapted to transmit collimated light to the first micro-electromechanical mirror.
 5. The optical switching element in claim 4, further comprising a lens positioned between the micro-electromechanical mirror and the lenslet array, wherein light reflected by the micro-electromechanical mirror is imaged on the lenslet array.
 6. The optical switch element of claim 1, wherein the micro-electromechanical mirror is a two-dimensional micro-electromechanical mirror.
 7. An optical switch device, comprising: (A) at least one source, the source being adapted to transmit an optical signal; (B) a plurality of targets, the targets being adapted to receive the optical signal; and (C) at least a first and second switch element, each switch element comprising a micro-electromechanical mirror positioned to receive light from the source, the micro-electromechanical mirror being adapted to selectively reflect light in a plurality of paths, the paths corresponding to the positions of the plurality of targets; and (D) a beam splitter positioned to reflect optical signals to the micro-electromechanical mirror of the first switch element, the beam splitter being adapted to reflect light within a predetermined range of wavelengths and allow light outside of the predetermined range of wavelengths to pass through the beam splitter, the second switch element being positioned to receive optical signals that pass through the beam splitter and transmit optical signals to the plurality of targets.
 8. The optical switch device of claim 7, wherein each switch element further comprises a controller in communication with the micro-electromechanical mirror, the controller being adapted to determine a target for an optical signal and cause the micro-electromechanical mirror to reflect light to the target.
 9. The optical switch device of claim 8, wherein each switch element further comprises a detector positioned to receive light from the source and in communication with the controller, the detector being configured to allow the controller to obtain information from an optical signal.
 10. The optical switch device of claim 7, wherein each switch element further comprises: (A) a beam splitter, the beam splitter being adapted to transmit light in a first predetermined polarization and reflect light in a second predetermined polarization; (B) a first wave plate positioned on an optical path between the source and the beam splitter, the first wave plate being adapted alter polarization of the light transmitted by the source so that it is reflected by the beam splitter, wherein light transmitted by the source passes through the wave plate and is reflected by the beam splitter; and (C) a second wave plate positioned between the micro-electromechanical mirror and the beam splitter, the second wave plate being adapted to alter polarization of the light reflected by the micro-electromechanical mirror so that it is transmitted by the beam splitter, wherein light reflected by the micro-electromechanical mirror passes through the second wave plate and is transmitted by the beam splitter.
 11. An array of optical switch elements, the array comprising: (A) at least a first and second switch element, each switch element comprising a micro-electromechanical mirror positioned to receive light from a source, the micro-electromechanical mirror being adapted to selectively reflect light into a plurality of paths, the paths corresponding to the positions of a plurality of targets; and (B) a beam splitter, the beam splitter being adapted to reflect light of a predetermined wavelength and allow light outside of the predetermined wavelength to pass through the beam splitter, the beam splitter being positioned to reflect light transmitted by a source to the micro-electromechanical mirror of the first switch element, the micro-electromechanical mirror of the second switch element being positioned to receive light that passes through the beam splitter.
 12. The optical switch device of claim 11, wherein each switch element further comprises a controller in communication with the micro-electromechanical mirror, the controller being adapted to determine a target for an optical signal and cause the micro-electromechanical mirror to reflect light to the target.
 13. The optical switch device of claim 12, wherein each switch element further comprises a detector positioned to receive light from the source and in communication with the controller, the detector being configured to allow the controller to obtain information from an optical signal.
 14. The optical switch device of claim 11, wherein each switch element further comprises: (A) a beam splitter, the beam splitter being adapted to transmit light in a first predetermined polarization and reflect light in a second predetermined polarization; (B) a first wave plate positioned on an optical path between the source and the beam splitter, the first wave plate being adapted to alter polarization of the light transmitted by the source so that it is reflected by the beam splitter, wherein light transmitted by the source passes through the wave plate and is reflected by the beam splitter; and (C) a second wave plate positioned on an optical path between the micro-electromechanical mirror and the beam splitter, the second wave plate being adapted alter polarization of the light reflected by the micro-electromechanical mirror so that it is transmitted by the beam splitter, wherein light reflected by the micro-electromechanical mirror passes through the second wave plate and is transmitted by the beam splitter.
 15. A method of switching optical signals, the method comprising the following steps: (A) providing at least a first and second switch element, each switch element comprising a micro-electromechanical mirror positioned to receive light from a source, the micro-electromechanical mirror being adapted to selectively reflect light in a plurality of paths, the paths corresponding to the positions of a plurality of targets; (B) causing light of a predetermined range of wavelengths to be received by the first switch element; (C) causing light outside of the predetermined range of wavelengths to be received by the second switch element; (D) determining a target to which to transmit the optical signal; and (E) causing the micro-electromechanical mirror in at least one of the switch elements to reflect the optical signal along a path, the path of the reflected optical signal corresponding to a position of a target, wherein the optical signal is transmitted to the target.
 16. The method of claim 15 further comprising: (A) wherein at least one of the first and second switch element further comprises a beam splitter, the beam splitter being adapted to transmit light in a first predetermined polarization and reflect light in a second predetermined polarization; (B) causing the optical signal to be polarized in the first predetermined polarization wherein the optical signal is reflected by the beam splitter to the micro-electromechanical mirror; and (C) causing the optical signal to be polarized in the second predetermined polarization, wherein light reflected by the micro-electromechanical mirror is transmitted by the beam splitter.
 17. An optical switch element for use with at least one source, the source being adapted to transmit an optical signal to the optical switch element, and a plurality of targets, the targets being adapted to receive the optical signal from the optical switch device, the optical switch device comprising: (A) a beam splitter, the beam splitter being adapted to transmit light in a first predetermined polarization and reflect light in a second predetermined polarization; (B) a first wave plate positioned on an optical path between the source and the beam splitter, the first wave plate being adapted to alter polarization of the light transmitted by the source so that it is reflected by the beam splitter, wherein light transmitted by the source passes through the wave plate and is reflected by the beam splitter; (C) a direction-altering device positioned to receive light reflected by the beam splitter, the direction-altering device being adapted to selectively direct light in a plurality of paths, the paths corresponding to the positions of the plurality of targets; (D) a second wave plate positioned between the direction-altering device and the beam splitter, the second wave plate being adapted to alter polarization of the light directed by the direction-altering device so that it is transmitted by the beam splitter, wherein light directed by the direction-altering device passes through the second wave plate and is transmitted by the beam splitter.
 18. The optical switch element of claim 17 wherein the direction-altering device comprises a micro-electromechanical mirror.
 19. The optical switch element of claim 17 wherein the direction-altering device comprises a gas bubble device. 